In fossil-fired power plants for generating electrical energy, an exhaust gas containing carbon dioxide occurs due to the combustion of a fossil fuel. This product is usually discharged into the atmosphere. The carbon dioxide which accumulates in the atmosphere obstructs the dissipation of heat from our earth and in this case leads to a rise in the earth's surface temperature due to what is known as the greenhouse effect. In order to achieve a reduction in the carbon dioxide emission in fossil-fired power plants, carbon dioxide can be separated from the exhaust gas.
Various methods are known, in general, for separating carbon dioxide from a gas mixture. The absorption/desorption method is customary especially for separating carbon dioxide from an exhaust gas after a combustion process.
The described separation of carbon dioxide by means of the absorption/desorption method is carried out on an industrial scale by means of a scrubbing agent. In a conventional absorption/desorption process, the exhaust gas is brought into contact in an absorption column with a selective solvent as a scrubbing agent. In this case, the uptake of carbon dioxide takes place by means of a chemical or physical process. The purified exhaust gases is purged from the absorption column for further processing or discharge. The solvent laden with carbon dioxide is conducted into a desorption column in order to separate the carbon dioxide and regenerate the solvent. Separation in the desorption column may take place thermally. In this case, the laden solvent is heated, a gas/vapor mixture of gaseous carbon dioxide and of the evaporated solvent being obtained, what is known as the exhaust vapors. The evaporated solvent is subsequently separated from the carbon dioxide. The carbon dioxide can then be compressed and cooled in a plurality of stages. In the liquid or frozen state, the carbon dioxide can then be delivered for storage or utilization. The regenerated solvent is conducted anew to the absorber column, where it can take up carbon dioxide again from the exhaust gas containing carbon dioxide.
The main problem in the existing methods for the separation of carbon dioxide from an exhaust gas is particularly of the very high energy outlay which is required in the form of heating energy for desorption. It has not hitherto been possible in the prior art to discover any useful improvements in this which would sufficiently reduce the energy outlay of a separating plant for the separation of carbon dioxide which is integrated into a power plant process.
In the chemical industry a multiplicity of extended circuit link-ups for saving heat energy in the desorption process are known. Thus, EP0133208 shows a method for assisting the regeneration of the absorbent in the desorber, what is known as the lean solvent flash method. EP1759756-A1 shows the lean solvent reheating method in which desorption process is assisted laterally. A circuit-link up disclosed in DE2817084-C2 assists the absorption process by means of side cooling. A further method for an extended circuit link-up is disclosed by patent specification DE1167318 as what is known as the split feed method.